Journal of Marine Biology I. A. U. Ahvaz – Spring 2014 –VOL.21 Effect of beach-seine catching activities on changes of substrate structure in the southern coast of the Caspian Sea (in Rudsar and Chaboksar) Shahpoor Gholamy1 Abstract Maryam Shapoori2* In this study, the effect of beach-seine catching activities on changes Karim Mehdi nejad3 of sediment structure of bed in Rudsar and Chaboksar areas were Zabih Alla Pajand4 investigated. Samples of sediment were taken monthly with a Van Veen grab covering a surface area of 225 cm2 from seining and non- 1, 2. Department of Natural fishing areas of Rudsar and Chaboksar stations in depths of 3, 6 and resources, Savadkooh Branch, 10 meters with 3 repetitions in each depth, in autumn and winter Islamic Azad University, 2011. The results show a significant difference between the Savadkooh, Iran percentage of silt-clay in the various sampling depths of seining area 3, 4. International Sturgeon Research Institute, Rasht, Iran and the percentage of silt-clay in the various sampling depths of non- fishing area, in each of Rudsar and Chaboksar stations and each of *Corresponding author: autumn and winter seasons (P< 0.05). So that, the amount of silt- [email protected] clay in seining area has been more than the amount of silt-clay in non-fishing area. In the Rudsar station, the amount of Total Organic Receive date: 2013.09.25 Acceptant date: 2014.02.24 Matter of the seining area were 2.6 and 2.2 percent in autumn and winter, respectively, and these amounts for non-fishing area were 2.3 percent in autumn and 1.7 percent in winter. Also in the Chaboksar station, the amount of Total Organic Matter of the seining area were 2.5 and 2.2 percent in autumn and winter, respectively, and these amounts for non-fishing area were 1.5 percent in autumn and 1.3 percent in winter. Results indicated a significant difference between the amounts of Total Organic Matter in seining and non-fishing areas (P< 0.05). Also, the amount of Organic Matter has significant and positive correlation with the percentage of silt-clay. The results of this study show the sediment texture of seining areas in the various sampling depths are different form non-fishing areas. Keywords: Beach-seine, Grain size, Bed, Rudsar and Chaboksar, Caspian Sea. 84.